Fold construction of corrugated fiberboard

ABSTRACT

This invention relates to fold line structure of a corrugated fiberboard in which the fold lines have a shape like the letter V, along which the corrugated fiberboard sheet is folded. The fold lines extend perpendicularly to or at an angle other than a right angle to the flutes. Each fold line is composed of cuts, each of which has a predetermined length and penetrates the corrugated fiberboard sheet, and hinge portions, each of which has a predetermined length and is formed by compressing the flutes, with the cuts and the hinge portions aligned in an alternating arrangement. Auxiliary cuts each have a planar shape approximating an one-sided arrow directed toward the adjacent hinge portion, penetrate the corrugated fiberboard sheet, and are formed on opposing sides at both ends of each cut portion. With the above constitution, the fold lines like the inverted letter V and the fold lines like the letter V can be formed on the corrugated fiberboard sheet through one process by the same die cutter, and the corrugated fiberboard sheet is able to be folded along the fold lines smoothly and accurately.

TECHNICAL FIELD

This invention relates to fold line structure of a corrugated fiberboard, in which the smooth, accurate folding of a corrugated fiberboard is enabled in the manufacture of a layered corrugated fiberboard structure of a predetermined shape or a porous hollow structure made of a corrugated fiberboard.

BACKGROUND ART

A technique of manufacturing a layered block structure id as shown in FIGS. 11 and 13, for example, has been already disclosed (See Japanese Patent Application No. Hei 6-103602). According to this technique, the layered block structure 1d is manufactured by the steps of forming fold lines like the inverted letter V, to which a directional folding property (i.e., an inclination to easily fold a corrugated fiberboard sheet) is imparted so as to allow the corrugated fiberboard sheet to fold in the shape of the inverted letter V (in a convex shape), and fold lines like the letter V, to which a directional folding property is imparted so as to allow the corrugated fiberboard sheet to fold in the shape of the letter V (in a concave shape), the two types of fold lines being parallel to each other in an alternating arrangement on the corrugated fiberboard sheet. The corrugated fiberboard sheet is then folded along the fold lines into a zigzag shape.

In addition, a technique of manufacturing a hollow block structure 1e as shown in FIGS. 14 and 15, for example, is disclosed in Japanese Patent Application No. Hei 7-237405. According to this technique, the hollow block structure 1e is manufactured by the steps of forming a plurality of fold lines like the inverted letter V and a plurality of fold lines like the letter V in parallel to each other in an alternating arrangement on a corrugated fiberboard sheet, and then folding the corrugated fiberboard sheet along the fold lines.

The layered or hollow block structure as described above is used as a frame structure or a cushioning material for packaging, a core material for a heat-insulating panel, a carrier for carrying adsorbents or the like.

In general, a corrugated fiberboard sheet is fabricated into a box by the steps of forming fold lines on the corrugated fiberboard sheet by pressing, and then folding the sheet along the fold lines.

In case of fabricating the corrugated fiberboard sheet into a box, the process of folding the sheet along the fold lines does not require high accuracy, and as a result, it is sufficient to form the folds by means of pressing. However, in the case where a layered or hollow block structure as described above is to be manufactured for the above purposes, there is a demand that such a block structure should be exact in shape and size according to the design. Thus, it is not possible to manufacture a block structure, which is fit for the above purposes, only by forming the fold lines in a manner similar to that in case of fabricating the corrugated fiberboard sheet into a box.

In the case where a layered block is manufactured by folding a corrugated fiberboard sheet in a zigzag shape along fold lines formed in advance on the corrugated fiberboard sheet, or a hollow block is manufactured by folding the corrugated fiberboard sheet, the following designs are generally adopted for fold lines, along which the corrugated fiberboard sheet is capable of being folded more accurately.

As shown in FIG. 8, for instance, in a first design fold lines 1a like the inverted letter V and fold lines 1b like the letter V are formed in parallel to each other, alternating between the two faces of the fiberboard sheet, in a halfway incised state (i.e., with cuts extending halfway through the thickness of the corrugated fiberboard sheet). The fold line cuts 1a, 1b intersect corrugated fiberboard flutes 10 and, subsequently, a directional folding property is given to each of the folds 1a, 1b by an appropriate folding mechanism (not shown).

As the result of giving the directional folding as described above, the fold lines 1a of the corrugated fiberboard sheet 1 shown in FIG. 8 take the shape of the inverted letter V, while the fold lines 1b take the shape of the letter V.

Japanese Utility Model Laid-open No. Sho 49-100981 shows a second design in FIG. 9 wherein halfway-incised fold lines 1a like the inverted letter V and fold lines 1b like the letter V are formed in parallel to each other in an alternate arrangement on a corrugated fiberboard sheet 1 such that the fold lines 1a, 1b intersect flutes. Each fold line 1b like the letter V is composed of a long linear cut 10a penetrating the sheet 1, and hinge portions 10b, 10b formed by compressing (crushing) the corrugated fiberboard sheet 1. A short auxiliary cut portion 10c, which extends perpendicularly to each cut 10a and penetrates the corrugated fiberboard sheet 1, is formed at each end of the cut 10a.

After the fold lines 1a, 1b described above are formed on the corrugated fiberboard sheet 1, a directional folding property is given to the sheet 1 along the fold lines 1a by imparting hinge portions 10b with the shape of the inverted letter V, while a directional folding property is given to the sheet 1 along the fold lines 1b by imparting hinge portions with the shape of the letter V, as shown in FIG. 10, by the use of an appropriate folding mechanism (not shown).

As the result of imparting the directional folding to the sheet 1 as described above, an inclination of the sheet to fold into the shape of the letter V is given to non-cut portions 10b of the fold lines 1b. Thus, when a transverse external force as viewed in FIG. 10 is applied to the sheet 1 so as to act in a direction perpendicular to the fold lines 1a, 1b, the sheet 1 is folded along the fold lines 1a, 1b as shown in FIG. 11, and as a result, the block structure id is manufactured.

The auxiliary cut portions 10c are formed in order to prevent the ends of the cut portions 10a of the sheet 1 from being broken when the directional folding property is given to the sheet 1 along the folds 1b.

A third design has been disclosed in International Laid-open No. W095/31330 and will be described with reference to FIG. 12. Halfway-incised fold lines 1a like the inverted letter V and fold lines 1b like the letter V are formed in parallel to each other in an alternate arrangement on a corrugated fiberboard sheet 1 such that the fold lines 1a, 1b intersect flutes 10. Each fold line 1b like the letter V is composed of linear cut portions 10a penetrating the corrugated fiberboard sheet 1, and hinge portions 10b formed by compressing (crushing) the corrugated fiberboard sheet 1. A short auxiliary cut portion 10d, which intersects each cut portion 10a to make an acute angle with the cut portion 10a and penetrates the corrugated fiberboard sheet 1, is formed at each end of the cut portion 10a.

The layered block structure id as shown in FIG. 13 is manufactured by imparting directional folding properties to the fold lines 1a, 1b, and then folding the corrugated fiberboard sheet 1 along the folds 1a, 1b.

The hollow structures shown in FIG. 14 or 15 are also manufactured by folding the sheet 1 along the fold lines 1a, 1b, and then bonding the portions folded along the fold lines 1a and portions folded along the fold lines 1b respectively together.

According to the first design described above, when the fold lines 1a, 1b are formed in the corrugated fiberboard sheet 1, it is necessary to make a cutting part (not shown) bite into both the surfaces of the sheet 1. However, a die cutter (not shown) ordinarily used for incising a corrugated fiberboard sheet is designed for the cutting part to bite into one surface of the corrugated fiberboard sheet 1 traveling along a line. Thus, when making an attempt to form a large number of fold lines 1a, 1b in the sheet 1 through one process, a specially-designed die cutter is needed, increasing the cost of the processing equipment.

On the other hand, in formation of the folds 1a on the corrugated fiberboard sheet 1 by one pass of the sheet 1 through a die cutter on a line, and subsequent formation of the folds 1b by passing the sheet 1 through the die cutter again after the sheet 1 is turned over, the required process steps are increased in number. In addition, due to the increase of equipment for adjusting the positions of the fold lines 1b, and other associated equipment, the manufacturing cost is increased.

Further, when a large number of fold lines 1a like the inverted letter V and a large number of fold lines 1b like the letter V as shown in FIG. 8 are formed on the corrugated fiberboard sheet 1, and directional folding properties are given to these folds, elasticity is lost in the folded portions to make it hard to fold or bend the corrugated fiberboard sheet in the final process, and it is difficult to fabricate the corrugated fiberboard sheet into a block structure again in case of reusing the corrugated fiberboard sheet.

According to the second design described above, it is possible to overcome the problems with the first design. However, the auxiliary cut portions 10c respectively extend perpendicularly to the cut portion 10a and are formed linearly, and all the non-cut portions 10b forming the hinge portions in the folds 1b are of equal length L within a width w corresponding to the length of each auxiliary cut portion 10c, as shown in FIG. 9. Thus, when directional folding properties are given to the sheet 1 along the folds 1b the hinge portions 10b formed as the non-cut portions are not always folded in alignment with the cut portion 10a with accuracy, and are somewhat offset from the cut portion 10a in some cases. Further, when the corrugated fiberboard sheet 1 is folded or bent after the directional folding properties are given to the sheet along the folds, the hinge portions 10b are bent somewhat away from the cut portion 10a in some cases. Therefore, when the sheet 1 is folded in layers as shown in FIG. 11, the folds 1a, 1b of the sheet 1 are slightly offset from each other as shown by arrows 1c in FIG. 11, and a layered block structure 1d easily gets out of shape. Thus, in some cases, it is not possible to manufacture a block structure 1d of a shape which is within the range of design tolerance.

According to the third design, since the auxiliary cut portion 10d at each end of the cut portion 10a has an angular shape pointed toward an adjacent hinge portion 10b, the pointed end of each auxiliary cut portion 10d serves as a guide in folding, and as a result, it is possible to fold or bend the corrugated fiberboard sheet 1 along the fold lines 1b with accuracy. However, in the case where the cut portions 10a respectively having the auxiliary cut portions 10d as shown in FIG. 12 are formed on the corrugated fiberboard sheet 1, it is necessary to manufacture a die cutting part (not shown) of a planar shape corresponding to the planar shape of each cut portion 10a by means of welding. The problem with manufacture of the die cutting part by means of welding is that the manufacturing cost of the die cutter (not shown) is increased.

Further, when a block structure is manufactured by folding the corrugated fiberboard sheet 1 along the fold lines 1a, 1b as shown in FIG. 13, or by bending the corrugated fiberboard sheet 1 along the fold lines 1a, 1b as shown in FIG. 14 or 15, a linerboard of the corrugated fiberboard sheet 1 protrudes from portions of the auxiliary cut portions 10d in folds formed at the fold lines 1b. The raised linerboard portions are sometimes obstructive to handling or broken when brought by contact with other objects. Sections of the corrugated fiberboard flutes 10 at portions of the cuts 10a are largely exposed, and as a result, the external appearance of the block structure 1d or 1e is damaged in some cases.

It is an object of the present invention to provide a design for fold lines shaped like the letter V, along which a corrugated fiberboard sheet is capable of being folded more accurately in manufacturing a layered block structure or a hollow block structure, in which a plurality of hollow portions are connected together by forming fold lines in the corrugated fiberboard sheet. and then folding or bending the corrugated fiberboard sheet along the fold lines.

Another object of the present invention is to provide a fold line structure for a corrugated fiberboard, in which corrugated fiberboard flutes are not largely exposed at the folds, and less linerboard protrudes from the folds, upon fabricating the corrugated fiberboard sheet into the block structure described above.

A further object of the present invention is to provide a fold line structure for a corrugated fiberboard, in which fold lines like the letter V, show sufficient elasticity for reuse of a corrugated fiberboard sheet.

DISCLOSURE OF THE INVENTION

According to a first embodiment of the present invention, there is provided a fold line structure in a corrugated fiberboard, in which a corrugated fiberboard sheet 1 has fold lines 12, along which the corrugated fiberboard sheet 1 may be folded, such that the folds 12 extend at an angle, i.e. a right angle or other angle, to flutes 10.

Each fold line 12 is composed of transverse cuts 12a, each of which has a predetermined length and penetrates through the corrugated fiberboard sheet 1, and hinge portions 12b, each of which has a predetermined length and is formed by compressing the flutes 10, the transverse cut 12a and the hinge portions 12b alternating in an aligned series forming the fold line 12.

Auxiliary cuts 12c, each of which, in cooperation with a transverse cut 12a, forms a planar shape approximating an one-sided arrow directed toward the adjacent hinge portion 12b and penetrates the corrugated fiberboard sheet 1, are respectively formed at both ends of each transverse cut 12a.

According to a second embodiment of the present invention, each intersection between a transverse cut 12a and an auxiliary cut 12c has the shape of a small circular arc.

According to a third embodiment of the present invention, the longitudinal distance Wl (parallel to flutes 10) from the cut 12a to the distal end of a joined auxiliary cut 12c is not more than the thickness t of the corrugated fiberboard sheet 1.

In the present invention, as long as each auxiliary cut 12c, in cooperation with the cut 12a from which it extends, forms an arrow shape directed toward the hinge portion 12b adjacent to the end of the transverse cut 12a, the auxiliary cuts 12c may have a linear shape, a circular-arc shape, or a bent shape.

When a corrugated fiberboard sheet is folded along the folds having the fold structure of the corrugated fiberboard according to the first embodiment of the present invention, a breaking stress concentrates at each intersection between each end of a transverse cut 12a and the auxiliary cut 12c joined at each end. Thus, it is possible to fold the corrugated fiberboard sheet 1 along the fold lines, smoothly and more accurately without breaking along the fold lines.

In the fold line structure according to the first embodiment, each auxiliary cut 12c is formed only on one side at each end of the cut portion 12a. Thus, in case of folding the corrugated fiberboard sheet 1 along the fold lines 12, there is much less exposure of the flutes 10 in the transverse cuts 12a, and much less linerboard raise from the auxiliary cut portions 12c.

The fold line structure according to the first embodiment shows sufficient elasticity to smoothly carry out machine working in the later folding process, and to allow easy reuse of the corrugated fiberboard sheet by unfolding the corrugated fiberboard sheet through the process of straightening at the fold lines, and then fabricating the unfolded corrugated fiberboard sheet into a block structure again.

A die cutting part of a cutter for forming the fold lines 12 according to the first embodiment is easily manufactured by the steps of cutting a tool steel sheet according to the design, then forming a cutting part before or after both ends of the tool steel sheet are bent, and then carburizing the cutting part.

In the fold line structure according to the second embodiment, since each intersection between a transverse cut portion 12a and an auxiliary cut 12a has the shape of a small circular arc, it is possible to fold a corrugated fiberboard sheet along the fold lines 12 more smoothly and decently.

In the fold line structure according to the third embodiment, since the distance wl from the cut portion 12a to the distal end of the auxiliary cut portion 12c is not more than the thickness t of the corrugated fiberboard sheet 1, the linerboard is hardly raised from the auxiliary cuts 12c in the corrugated fiberboard sheet when folded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary plan view showing a fold structure of a corrugated fiberboard in an embodiment according to the present invention;

FIG. 2 is an enlarged-scale perspective view showing a cutting die used for forming fold lines according to the embodiment shown in FIG. 1;

FIG. 3 is a fragmentary perspective view of the corrugated fiberboard sheet folded along the fold lines shown in FIG. 1;

FIG. 4 is a fragmentary perspective view showing a corrugated fiberboard sheet bent along a fold line shown in FIG. 1;

FIG. 5 is a fragmentary plan view showing a fold line structure in another embodiment according to the present invention;

FIG. 6 is a fragmentary plan view showing a fold line structure in a further embodiment according to the present invention;

FIG. 7 is a fragmentary plan view showing a fold line structure in a still further embodiment according to the present invention;

FIG. 8 is a fragmentary perspective view showing a prior art fold line structure in corrugated fiberboard;

FIG. 9 is a fragmentary plan view showing a fold structure as described in Japanese Utility Model Laid-open No. Sho 49-100981;

FIG. 10 is a fragmentary perspective view showing directional folding properties in the corrugated fiberboard sheet shown in FIG. 9;

FIG. 11 is a fragmentary perspective view showing a block structure manufactured by folding the corrugated fiberboard sheet shown in FIG. 10 along the fold lines;

FIG. 12 is a fragmentary plan view showing a fold line structure of a corrugated fiberboard described in International Laid-open No. W095/31330;

FIG. 13 is a perspective view showing a block structure manufactured by folding the corrugated fiberboard sheet shown in FIG. 12 along the fold lines;

FIG. 14 is a fragmentary front view showing a hollow block structure manufactured from a corrugated fiberboard sheet; and

FIG. 15 is a fragmentary front view showing another hollow block structure manufactured from a corrugated fiberboard sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a corrugated fiberboard sheet 1 has a large number of fold lines 11, along which the corrugated fiberboard sheet 1 is folded in the shape of the inverted letter V, and a large number of fold lines 12, along which the corrugated fiberboard sheet 1 is folded in the shape of the letter V. The fold lines 11, 12 are formed at a repeating interval, in parallel with each other and extending perpendicular to flutes 10.

The fold lines 11 like the inverted letter V and the fold lines 12 like the letter V have the same constitution, except that the corrugated fiberboard sheet is folded in opposite directions along the fold lines 11, 12 respectively.

Each fold line 12 (or 11) is composed of transverse linear cuts 12a penetrating the corrugated fiberboard sheet 1 and hinge portions 12b formed by compressing the flutes 10 of the corrugated fiberboard sheet 1. The cuts 12a and the hinge portions 12b are formed alternately in a row. Hinge portions 12b are respectively placed on both side edges of the corrugated fiberboard sheet 1.

Auxiliary cuts 12c each have the planar shape of a one-sided arrow directed toward the adjacent hinge portion 12b and penetrate the corrugated fiberboard sheet 1. Auxiliary cuts 12c are respectively formed on the reverse side at both ends of each cut 12a such that the auxiliary cuts 12c are continuous with the cuts 12a.

A junction between the auxiliary cut 12c and the cut 12a in the fold lines 12 of this embodiment is pointed and the auxiliary cut 12c and the cut 12a intersect each other at an angle smaller than a right angle. A portion of the junction between the cut portion 12a and the auxiliary cut portion 12c has the shape of a small circular arc.

In this embodiment, the corrugated fiberboard sheet 1 has a corrugating medium provided with B-flute (composed of 50+2 flutes per 30 cm) and is designed such that the cut 12a and the hinge portion 12c are respectively 15 mm in length, the auxiliary cut 12c is 3 mm in length, and the junction intersection between the cut portion 12a and the auxiliary cut portion 12c is approximately 1 mm in circular-arc diameter. Further, the distance wl from the cut 12a to the distal end of the auxiliary cut portion 12c is smaller than the thickness t (See FIGS. 2 and 3) of the corrugated fiberboard sheet 1, i.e., 3 mm or less.

A directional folding property is given to the fold lines 11 so as to allow the corrugated fiberboard sheet 1 to be folded into the shape of the inverted letter V along the fold lines 11, and likewise, a directional folding property is given to the fold lines 12 so as to allow the corrugated fiberboard sheet 1 to be folded into the shape of the letter V along the fold lines 12. In this manner, the corrugated fiberboard sheet 1 is folded as shown in FIG. 3 or bent as shown in FIG. 4.

The fold lines 11, 12 of the corrugated fiberboard sheet 1 in this embodiment may be formed simultaneously by the use of a die cutter (not shown) including a press piece and a cutter 2 which bites into one surface of the corrugated fiberboard sheet 1.

The cutter 2 has a main cutting part 20 and integrally-bent auxiliary cutting parts 21 formed at both ends of the main cutting part 20, as shown in FIG. 2. The cuts 12a are formed by the main cutting part 20, and the auxiliary cuts 12c are formed by the auxiliary cutting parts 21.

The cutter 2 shown in FIG. 2 is manufactured by the steps of cutting a tool steel sheet which is provided with a linear cutting edge, in a predetermined shape, then annealing and bending the cut steel sheet, and thereafter finishing the bent steel sheet by means of carburizing.

According to this embodiment, the auxiliary cuts 12c having the planar shape of a one-sided arrow directed toward the adjacent hinge portion 12b are respectively formed at both ends of each linear cut 12a, as described above. The shortest possible length in the transverse direction for each hinge portion 12b is along a line corresponding to the intersection between the adjacent cut portion 12a and the auxiliary cut portion 12c, i.e., a central portion in the cross direction of the hinge portion in this embodiment. Therefor, when the corrugated fiberboard sheet 1 is folded along the fold lines 11, 12 by applying a bending pressure from an apparatus (not shown) to the corrugated fiberboard sheet 1, each intersection between the cut 12a and the auxiliary cut 12c serves as a guide in folding. Thus, the corrugated fiberboard sheet is folded from the intersections or junctions, and as a result, it is possible to accurately fold or bend the corrugated fiberboard sheet 1. Further, bending stress is concentrated at the small circular arc-shaped portions of the junctions between the cuts 12a and the auxiliary cuts 12c. Accordingly, portions other than these junctions are prevented from being broken when the corrugated fiberboard sheet is folded.

The corrugated fiberboard sheet 1 is folded along the fold lines 12 as shown in FIGS. 3 and 4. In this state, there is much less opening of the cut portions 12a, and much less exposure of the flutes 10 in the cut portions 12a. Further, since the distance wl from the cut portion 12a to the distal end of the auxiliary cut portion 12c is smaller than the thickness t of the corrugated fiberboard sheet 1, a linerboard of the fiberboard hardly protrudes from the auxiliary cut portions 12c when folded along the fold lines 12.

The hinge portions 12b in the fold lines 12 show elasticity sufficient to easily carry out mechanical folding work, and to easily fabricate the corrugated fiberboard sheet 1 into a block structure again in case of reusing the sheet 1 by unfolding the sheet 1 into a flat shape through the process of straightening the folds 11, 12, after the sheet 1 has been used.

Since the cutting part 2 of the die cutter (not shown) is simply formed by bending as shown in FIG. 2, a cutting part of a die cutter in existing equipment may be exchanged for the cutting part 2 in use, and as a result, its fabricating equipment is less expensive.

Other Embodiments

In the above embodiment, the auxiliary cut portions 12c are respectively formed on opposite sides at both ends of each cut portion 12a. Otherwise, the auxiliary cut portions 12c may be formed on the same side at both ends of each cut portion 12a, as shown in FIG. 5.

In the above embodiment the auxiliary cut portions 12c are formed linearly. Otherwise, the auxiliary cut portions 12c may have a circular-arc shape as shown in FIG. 6, or a bent shape as shown in FIG. 7, and the effects in either case are similar to those of the above embodiment.

According to the fold line structure of the corrugated fiberboard in the present invention, it is possible to fold the corrugated fiberboard sheet more accurately along the fold lines, along which the corrugated fiberboard sheet is folded in the shape of the letter V. In addition, it is possible to prevent the corrugated fiberboard sheet from being broken when the corrugated fiberboard sheet is folded.

Further, when the corrugated fiberboard sheet is folded along the fold lines, there is much less exposure of the flutes in the folds, and much less linerboard protrusion at the auxiliary cut portions. As a result, the folds present a good appearance, and the corrugated fiberboard sheet is prevented from breakage even after the corrugated fiberboard sheet has been processed. 

What is claimed is:
 1. A corrugated fiberboard sheet having a longitudinal dimension, a transverse dimension and a thickness, comprising:an intermediate layer with flutes extending along the longitudinal dimension of the corrugated fiberboard; first V-shaped fold lines in one surface of the transverse dimension of the fiberboard sheet and across the flutes at an angle; a series of separate linear slits in each of said first fold lines penetrating the corrugted fiberboard sheet, in each of said first fold lines said slits alternating and aligned with, in a straight line, uncut portions of said first fold lines, said uncut portions serving as hinges for bending the corrugted fiberboard sheet at said first fold lines; and linear auxiliary cuts joined at an angle to each of opposing ends of each of said slits, each of said auxiliary cuts forming, in cooperation with a joined slit, an one-sided arrow directed toward an adjacent hinge, each of said ends of said slits having only a single auxiliary cut which extends only in a single direction in the longitudinal dimension and in an opposite direction, along the transverse dimension, from the auxiliary cut on the other end of said slit
 2. A corrugated fiberboard according to claim 1, wherein said auxiliary cuts join said slits at junctions in the shape of a circular arc.
 3. A corrugated fiberboard according to claim 1, wherein the distance in the longitudinal dimension from a slit to a distal end of an auxiliary cut joined thereto is at least the thickness of the corrugated fiberboard sheet.
 4. A corrugated fiberboard according to claim 1 further comprising:second V-shaped fold lines in a second surface of the fiberboard sheet and extending in a straight line across the transverse dimension of the fiberboard sheet and across the flutes at an angle, said second fold lines alternating with and spaced from said first fold lines along said longitudinal dimension; and a series of separate linear slits in each of said second fold lines penetrating the corrugated fiberboard sheet, in each of said second fold lines said slits alternating and aligned with, in a straight line, uncut portions of said second fold lines, said uncut portions serving as hinges for bending the corrugated fiberboard sheet at said second fold lines.
 5. A corrugated fiberboard sheet according to claim 1 wherein auxiliary cuts joined to opposing ends of one of said slits in one of said fold lines extend in the same first direction along the longitudinal dimension.
 6. A corrugated fiberboard sheet according to claim 5 wherein auxiliary cuts joined to opposing ends of a second of said slits in said one fold line extend in the same second direction, opposite said first direction, along the longitudinal dimension and wherein said first and second slits alternate within said one fold line.
 7. A corrugated fiberboard according to claim 1 wherein auxiliary cuts joined to opposing ends of one of said slits extend in opposite directions along the longitudinal direction.
 8. A corrugated fiberboard according to claim 1 wherein said angle is an acute angle. 